Various tissue sites within the human body are susceptible to injury, deterioration and disease. Tissues located at orthopedic joints, organs and various connective tissues are often damaged as a result of injury or surgical procedures, often producing ruptures and apertures in the tissue. For example, such apertures (e.g., the surgical opening and/or removal of tissue) can be created as a result of herniation or biopsy locations. Short-term and long-term structural and functional integrity of tissue is often an important consideration in arthroscopic surgery, especially in those situations where the apertures are slow to close and heal.
The intervertebral discs, which are located between adjacent vertebrae in the spine, provide structural support for the spine as well as the distribution of forces exerted on the spinal column. An intervertebral disc consists of three major components: cartilage endplates, nucleus pulposus, and the annulus fibrosus. The central portion, nucleus pulposus, is relatively soft and gelatinous, being composed of about 70 to 90% water. It has a high proteoglycan content and contains a significant amount of Type II collagen and chondrocytes. Surrounding the nucleus is the annulus fibrosus, which has a more rigid consistency and contains an organized fibrous network of approximately 40% Type I collagen, 60% Type II collagen, and fibroblasts. The annular portion serves to provide peripheral mechanical support to the disc, afford torsional resistance, and contain the softer nuclear portion and resist its hydrostatic pressure. A number of other functions which the annulus fibrosus can perform are discussed in Kusaka et al., "The Effect of Annulus Fibrosus Perforation of the Intradiscal matrix Strain of the Axially Loaded Intervertebral Disc", Transactions of the 44.sup.th Annual Meeting of the Orthopedic Research Society, New Orleans, La., Abstract 190-32, (March 1998).
Intervertebral discs are, however, susceptible to a number of injuries. Disc herniation occurs when the nucleus begins to extrude through an opening in the annulus, often to the extent that the herniated material impinges on nerve roots in the spine. The posterior and posterio-lateral portions of the annulus are most susceptible to attenuation or herniation, and therefore, the most vulnerable to the hydrostatic pressures exerted by vertical compressive forces on the intervertebral disc. Various injuries and deterioration of the intervertebral disc and annulus fibrosus are discussed by Osti et al., Annular Tears and Disc Degeneration in the Lumbar Spine, Journal of Bone and Joint Surgery, 74-B(5), September 1992 pp. 678-682; Osti et al., Annulus Tears and Intervertebral Disc Degeneration, Spine, 15(8) (1990) pp.762-767; Kamblin et al., Development of Degenerative Spondylosis of the Lumbar Spine after Partial Discectomy, Spine, 20(5) (1995) pp. 599-607.
Many treatments for intervertebral disc injury have involved the use of nuclear prostheses or disc spacers. A variety of prosthetic nuclear implants are known in the art. For example, see Bao et al., U.S. Pat. No. 5,047,055, which teaches a swellable hydrogel prosthetic nucleus. Other devices known in the art, such as intervertebral spacers, use wedges between vertebrae to reduce the pressure exerted on the disc by the spine. Intervertebral disc implants for spinal fusion are known in the art as well, as taught by Brantigan, U.S. Pat. Nos. 5,425,772 and 4,834,757. In spite of these advances in treating the overall disc, remaining problems include the effective repair or restructuring of annular tissue, per se. This is true regardless of whether the annular tissue has been damaged by herniation, or by the creation of surgical access ports in the course of disc repair. This is primarily due to the avascular nature of the annulus, and partly due to the difficulties associated with hydrostatic pressure exerted on the entire disc by the compressive forces on the spine. For example, see Hampton et al., Healing Potential of the Annulus Fibrosus, Spine, 14(4) 1989, pp.398-401 which discusses some of the difficulties encountered in such repairs.
On a separate subject, natural and synthetic porous materials which enhance or encourage natural tissue growth are known in the art. For example, see Burg et al., "Modulation of Surface and Bulk Properties of Biomedical Polymers", Annals New York Academy of Sciences, 831 (1997) pp.217-222; and Vacanti et al., U.S. Pat. No. 5,716,404. A number of implantable devices that involve the use of expandable materials are also known. For example, Cobey, Milton C., "Arthroplasties Using Compressed Ivalon Sponge ("Intramedic Sponge", Clinical Orthopaedics and Related Research, No.54 (September-October 1967) pp. 139-144 teaches an implantable plastic sponge material used on joint surfaces which induces fibrous tissue ingrowth. See also Stone, U.S. Pat. No. 5,258,043, which teaches a prosthetic intervertebral disc that functions as a scaffold for tissue ingrowth.
On yet another subject, Applicant has described prosthetic implants formed of biomaterials that can be delivered and cured in situ using minimally invasive techniques. See, for instance, Applicant's U.S. Pat. No. 5,556,429, and published International Application WO 95/30388. Applicant's published International Application WO 97/26847 and International Application No. PCT/US97/20874, filed Nov. 14, 1997, (the disclosures of each of which are incorporated herein by reference) further describe, inter alia, the formation of a prosthetic nucleus within an intervertebral disc by a minimally invasive method that includes, for instance, the steps of inserting a collapsed balloon mold prosthesis through a cannula that is itself positioned through an opening within the annulus, and filling the balloon with a flowable biomaterial that is adapted to cure in situ and provide a permanent disc replacement.
Although a number of prosthetic intervertebral discs, nuclear implants, and disc spacers are known in the art, relatively little attention has been focused on effectively sealing an opening in the annulus which has either been initiated surgically, such as an access port for a minimally-invasive technique, or caused naturally, as in the case of herniation.